Neither estrogen or the antagonist should change your luteal phase; any changes while on EPP are not due to those particular meds because they don't effect your progesterone production. What they do is shut down your ovaries so that no preliminary follicles can start to grow (your body normally starts recruiting follies in your LP) and thus, when you actually start your stims, your antral follicles are all close to (or closer to) the same size, thus discouraging lead follicles. Because you're suppressed, many people on EPP will stim longer and slower than on a straight non-suppression cycle. For me the difference was a few days longer.
Something about how estrogen works: your developing follicles naturally make estrogen. It's what makes your lining plump up and also what makes your body shut off it's FSH production. Interrupring this feedback loop is how Clomid and Letrozole work to get your body to overproduce FSH. This is also why cd3 FSH values need to be interpreted with E2 in mind. If your E2 is unnaturally high because of a cyst or because that's how your body rolls, it will make your FSH unnaturally low and make you appear more fertile than you really are. When you are doing EPP your cd3 E2 will be pretty high and your FSH will be really low, like maybe less than 3.
Digi pizza is gluten free, dairy free and deelicious I assume?