In a code language, DOCUMENT is written as FRGUMWQH. How is PERCEIVE written in that language?

Given that  DOCUMENT is written as FRGUMWQH

PERCEIVE written in that language

We know that alphabet position A=1, B=2, C=3, D=4 ....... Z=26

represent in the form of alphabet position 

4 15 3 21 13 5 14 20

6 18 7 21 13 23 17 8

the pattern is going on first three alphabet position cross add +3, +3,  and middle add +3 and middle two alphabet position written as same  last three alphabet position cross add +3, +3 middle add +3 

similarly, PERCEIVE

written as alphabet position 

16 5 18 3 5 9 22 5 is 

the pattern is going on first three alphabet position cross add +3, +3, and middle add +3 and middle two alphabet position written as same last three alphabet position cross add +3, +3 middle add +3

(16+3) (5+3) (18+3) (3) (5) (5+3) (22+3) (9+3)

21 8 19 3 5 8 25 12

represent in the form of alphabet

U H S C E H Y L Ans