Unless i'm cutting a through joint, I don't worry about it. A couple of reasons... First, gluing has no effect on end grain and the mortise ends of your joints are end grain. Second, go ahead and add a little extra glue... it will simply collect in the unfilled end (round) portion of the mortise. When cutting mt joints, I like making my tenons a wee bit fat and use a metal file to hone them down to perfection ( assemble with hands only [no pounding], when picking up the unglued joint, it holds and you should disassemble the dry fit with hands only and no punding).
Its' never hot or cold in New Hampshire... its' always seasonal.