anyone a car sprayer on here? need advice

[tovtm]

Hi I've got a rusty rear wheel arch that in in the process of sorting out so far I've sanded back the rust filed and sanded and primed. The car is a Toyota celica 2000> matallic silver. You can see from the picture I've drawn where I've repaired so should I be blending to a certain point/spraying

I need to know If to match the new spray with the old if I should blend the spray past the filler by ....??? Inches iveheard alot about halo but not sure what causes it.

Is there any process I should go through? I'm using cellulose so 50/50 mix with thinners