Tighter, yes, due to added tension. Normally tunings are named by the lowest pitched string (as might be with re-entrant), C6, D6, G6, etc and then 'specified'
re-entrant for a high-4th string or
linear for a low-4th string.
Thus your 'low A tuning' is usually called 'D6' tuning because in re-entrant the lowest pitch string, i.e., the 3rd string is tuned to D.
I'd be cautious about tuning up to D6 (A-D-F#-B) on a tenor and would keep an eye on the bridge and see if it is 'rotating' forward. Check it every couple of hours.
If so you will see dishing (a dip or valley betw the bridge and sound hole) as well as bellying (a hump or ramp from the butt end to the bridge). On some lightly built ukes, a little of this is ok, but if it's really obvious, or you seen the tail end of the bridge pulling up, that is a bad sign, and I'd back off to tuning or use lower tension (thinner gauge) strings...
YMMV. Most of the tales of D6 tuning I've read are with a soprano, which has about 50% of the total string tension of a tenor due to the shorter scale length.
Tension is a funny thing in that you may not see the effects until just before it all goes bad, like right before the bridge, and usually a chunk of wood from the top, gets torn off.
I hope nothing bad happens. Good luck!
