Xin:After vacation I once again want to meet someone. Thinking again about speed dating thing.
Question: what can I ask a woman (not straightforward) to get a clue that she is into big guys, might be a potential ffa and would like or at least tolerate that feederism thing even if she's not aware. All that in 3-5 minutes

Perhaps something like "...I guess maybe you're looking for someone a little slimmer or more athletic?" and "...guess I do like to eat, probably why I've put on a few pounds". Listen carefully to her response, you'll probably be able to tell whether she's just being polite or whether she's genuinely ok with it.
Just remember, you've only got 3 minutes and you'll probably never meet them again so don't worry about being too shy about it all.