In addition to what meindzai said (btw, good to see you around once again meindzai, how's Florida?)
Perhaps it's the English term "form" that's confusing because it can designate such things as shape of an object (e.g. square, round, etc), or a complex object (a car, a house, etc), which are basically conceptual (perhaps that's what you mean by "a hypothesis"). But in abhidhamma framework "form" would be basically a translation for the pali term rupa, which would usually stand in for all dhammas that belong to the rupa class of dhammas. And there are all together 4 classes of dhammas - rupa (form or material phenomena), citta (consciousness), cetasika (mental factors) and nibbana (the only one which is unconditioned).
It's further said that there are all together 31 (if I remember right) different dhammas that belong to the rupa class. Some of these can be directly experienced by becoming an object of a sense-consciousness (touch, smell, taste, hearing, seeing), while some can only be an object of mind-consciousness. So for example, as meindzai mentioned, the 3 elements of earth, fire and wind can be experienced through touch (tactile-consciousness) as hardness, heat and motion, while the element of water can be experienced thought mind-consciousness as cohesion.
Anyway, chapter VI (page 234) is specifically on rupa in - the link takes you to a free online version of the book on google books. In fact, you might find reading the whole book helpful as it addresses many of the issues you've been interested in lately.
There's also a book by Nina Van Gorkom just about rupa - also free online reading .