I've never heard this thing about pollen grain size being a factor. However, I don't "hear" everything either.
Of course, it would have to be the size of the pollen tube the emerges from the pollen grain to penetrate the stigma that might be a factor, rather than the actual size of the pollen grain itself, I would think. And I suppose it might make sense that large pollen grains would produce larger pollen tubes. Whether this is true or not, I don't know, and I suspect that, as in most cases, there is variation.
Talking about actual surface area of a stigma versus a cut style, of course the stigma would have more (being larger). I think we are talking semantics here, and the real (possible) difference is the entry surface make up, which might be chemically and/or physically different. And the physical difference could well include an acceptance of larger pollen grains/tubes.
Regarding a need for a cut style in relation to style length, I think there are variables. In closely related pod parents, I would think a cut style would only be needed if the pod parent's style was at least 1.25 times the length of the pollen parent's stlye. However, if the pod parent is more distantly related, the chemical make up of the style may be more difficult for the pollen tube to penetrate. I don't know. Again, at any rate the advantage of a style cut in half versus one cut near the stigma end is more likely.
Frankly, I don't see why you would have such difficulty crossing those two pictured (A7, A9) via simple pollination. Did they really have significantly different sized pollen grains? Much surprise here. And if those are indeed hybrids to begin with, surely there would be no problem hybridizing them with the traditional method. Perhaps weather conditions did not cooperate in prior attempts. L. regale, literature purports, is a reluctant hybridizing pod parent, and seems to prefer apomixis.
l see tell tale signs of borderline fasciation on A9: the groovings in the stem that terminate with the individual flower stems. Fasciation doesn't have to produce flat stems, and it is not necessarily a bad thing. The phenomenon is such an enigma that it is difficult to tell where it begin or ends! So I am not sure if the high bud count can/will be transmitted genetically. However the pedicel form is fairly elegant (although I have seen more pronounced S shapes), and a worthy trait to impart if A7 has straight or down turned pedicels. BTW, I really love A7's tepal form.
