help needed with ARE CX series cap.....

hi folks,
just bought today a used CX series cap for my 2015 2nd gen (access cab, 6ft bed). cap is in excellent shape and seems to fit like a glove. only concern is.....
along the front edge of the cap, running overtop of the bed rail from side to side, there is a vertical gap...a gap of about 3/4-1" from the undersurface of the cap and the top surface of the bed.
it's almost as if there should be a spacer or something running side to side to fill this void. yet, there is the squishy foam tape stuff on the bottom surface of the cap, as if that came in contact with the bed (during the prior owner's installation).

i'm 100% confident the cap is installed properly, i'm a pretty mechanically savvy guy. both sides of the cap are resting firmly on top of the bed rails, and it clamped down properly.
something funky going on along that front edge....i have to be missing something!?
any ideas about this?

i'm nearly 100% certain the cap is for a 2nd gen tacoma and not something else. i've researched this a lot.
the prior owner is not able to be contacted for questions (or at least not worth contacting as they didn't seem very knowledgeable).


low quality pic but hoping this might help to visualize.

many thanks for any help.

 

maybe not the right cap for your truck but....get ya length of that soft rubber black foam pipe covering and slit it open. fit it in there and crank down on that. might wanna glue it somehow to the rail first. cap looks like it fits good except for that.

 

Last fall I purchased the exact topper for my 2015 AC. Before they installed the topper the dealer placed a piece of rubber seal on the front rail edge to fill the gap. This is normal.

Amazon sells the stuff: Front-Rail-Seal-EPDM-Rubber Seal

 

thank you everyone, good to know nothing unique about my situation. this was driving me nuts!