Actually, you couldn't be further from the truth.
Mace does not reflect anything back at Palpatine.
He simply absorbs it with his sword, like Obi does with Dooku in AOTC.
Then he closes in on him, trying to force him out of the window he has intentionally broken.
Eventually he is so close that the lightning is being fired at point blank range so it begins to arc back at Palpatine himself.
It is just the proximity that causes the damage.
Yoda, however - despite being caught off guard by Palps opening salvo - seems to be the only Jedi able to counter Sith lightning with his bare hands, which he does against Dooku in AOTC and again against Palaptine in ROTS.
The Force swells in front of them before exploding, sending both combatants reeling from the senate pod.
Originally posted by ShadowKing
Up to the point he is hit, I don't know if Yoda realizes Palpatine is Sithy.
Did Mace get to let Yoda know before he confronted him? He def did not get a chance to let him know afterward...
Yoda has just watched footage of Anakin being knighted a Dark Lord of the Sith by Sidious - in Palpatine's office, in Palpatine's clothes.
I'd say he has a pretty good idea 😉