Find the letters which complete the patterns

The following five series follow the same pattern. Fill the missing letters in each of them:

Puzzle 1:
"Using" is E
"Desist" is I
"Visits" is E
"Design" is ???

Puzzle 2:
"Asia" is H
"Cuffs" is S
"Ender" is I
"Redness" is F
"Fuchsia" is ???

Puzzle 3:
"Pro-tem" and "row" are H
"Ties" is K
"Cohesion" is A
"Casino" is E
"Hocks" is either a word, name, ??? or ???

Puzzle 4:
"Gross" is W or R
"Assign" is S
"Amassing" is E
"Design" is S
"Amassing" is S
"Arrows" is ??? or ???

Puzzle 5:
"Edna" is I
"Slang" is X
"Siege" is E
"Basin" is X
"Sin" is X
"Sin" is A
"Besiege" is X
"Signals" is ??? and ???

Each "puzzle" is a palindrome. For example, the sentence "using is e desist is i visits is e design is ???" should be the same read from left to right and from right to left. Therefore the missing letters are:
"U", "A", "T" or "P", "S" or "G", "I" and "E".