Small Batch in 6.5 Primary. . .

Didn't know exactly how to label the question. . .

I am looking at making a few small batches of cider, experimenting with beer, etc. and my question is can I go ahead and do the primary fermenting in my regular 6.5 plastic bucket even if I am only making 2-3 gallons are so, and then put in my 1-3 gallon glass carboys as I experiment? Just curious if I should be primary fermenting in a vessel that is closer to the actual volume of liquid.

May be a dumb question, but throwing it out there. Thanks.

Yes, there should be no problem the head space will be filled with co2.

Appreciate that, thought it would be fine, but you never know.