I've been looking, but the only papers I've found have been on the effectiveness of mycos in field situations, but nothing on comparing the effectiveness of delivery methods.
The only thing I found was a couple of sentences in a Dr. Jimz blog about why they decided not to use a liquid or a powder when making their own myco supplement, so I wouldn't necessarily give much weight to that.
I'm still curious as to how many of the spores can reach the deeper portions of the root system when watered in.
I'm not disputing that some of them can, just questioning the efficiency of this method of applying them.
I haven't been able to find any studies on it, but my research skills are lacking after so many years out of school.
As long as the spores come into direct contact with the roots it should work.
The only really consistent info I've found is that a) they're helpful b) they take a month to colonize a root system and c) microbes can suppress their growth, but they have no effect on microbe populations.
It's great to have these discussions! I'm going to keep looking for info on how different spore delivery systems work. If I find anything I'll let you know. I can't believe that there hasn't been some study done on the subject given the number of products there seem to be containing mycos.
I’ve noticed the same thing regarding the studies and it’s started making me suspicious. I don’t like the lack of information. The best I’ve found so far is this from teaming with fungi:
“Most commercial mycorrhizal products include specific directions that should be followed. These inoculation methods may differ, but they all have one thing in common: as many of the fungal spores as possible must be located in a position that ensures that they will receive the host plant’s chemical signals, which prompt the spores to branch their hyphal extensions and enter into mycorrhizal relationships with the roots. Without a signal from the plant, the mycorrhizal spores may germinate, but it will not colonize and it will not benefit the plant.
There are three types of formulations of arbuscular mycorrhizal propagules, a combination of spores and hyphal
fragments that contain arbuscules, which can act like spores. All three formulations can comprise the same spores, but the delivery method is different.
Propagules mixed with granular substances: These mixes are spread into soil or other planting media and onto roots in various ways.
Propagules mixed in soil: These are natural soils that contain known mycorrhizal fungi. It is possible to make your own soil fungi mix using plant root fragments.
Propagules mixed in liquid: The liquid formulation is an important innovation that increases the uses of mycorrhizal fungalspores: they can be used in drip and irrigation systems and delivered to existing plants.
Formulations vary in the particular genus and species of included fungal spores. One size does not fit all. This is why it is vitally important that before applying the inoculant, you read the label and know what is included in the mixture. Make sure you are using the appropriate type of fungi to match the host plant, that the product is viable, and that the packaging offers a general idea of the numbers of spores involved—not so much for viability concerns, but for your own record keeping. You may have to experiment with various formulations and doses, so keeping good notes can help ensure that you settle on the best application methods and amounts.
The best way to establish arbuscular mycorrhizae in agricultural situations is to inoculate seed just before planting.
This ensures that the plants can take advantage of mycorrhizal benefits from the first day after germination.
Inoculant application methods vary depending on the situation at hand.
Seed inoculation Seeds can be rolled in granular and powdered formulations or sprayed with liquid formulas. Spraying seed with water first will help granular mixes adhere.
Seed germination mix inoculation All formulations can be used in the soil in which seeds are germinated. Seed starting cubes, transplant cubes, and growing media for hydroponics can all be inoculated with granular or liquid formulations. Because mycorrhizal fungi thrive in a pH range of 5.5 to 7.0, the media used must have the proper pH to sustain the inoculant.
Bare-root inoculation Bare plant roots can be sprayed, sprinkled with, or dipped into any of the formulations
and inoculation will result.
Bare-root soil inoculation Planting bare-root plants in soil that already contains arbuscular mycorrhizal propagules will result in the formation of mycorrhizae.
Transplant inoculation Both liquid and granular formulations can be applied to the plant roots at transplanting
time. In addition, spores can be mixed into transplanting soil using any of the formulations.
Root inoculation All formulations can be used to feed roots of existing plants, as long as they contact the roots. Liquid formulations can usually be applied to the surface. Granular and soil mixes can be placed on the surface for plants with shallow roots in loose soils, but for deeper roots it is best to provide channels to the root zone. Packing these with granular or soil mixes allows for the root to fungi signaling required for the formation of arbuscular mycorrhizae”
however, 
I can see that causing an issue. If for no other reason than possible compaction from setting the plants down a little too hard.
anything’s possible 
(oh boy there goes Keffka, again, probably stoned, again)
