Advice on irons off tees

Hi All , might b a silly question to ye who have always did this , but.......
Iv been trying to practice playing par 3 tee shots off a tee , up to now ive played off the grass ,
i notice im hitting it higher and as a result shorter .. Should i b using a club more because im using a tee or am i maybe teeing it a fraction high ? Maybe angle of attack is wrong?
has any1 else changed like this ?
do u still compress the ball or sweep it off the tee ?

Gona try get it right over the winter so any tips would be appreciated
Thanks in advance ..