As requested by Tim Hobson on the forums
I have two sets of certs installed, one dev , one prod
<4.9.2 part>
create new project - thirdPerson Blueprint
Mobile / Max Quality / With Starter
In Level
Lighting/Lightsource Actor - set cast modulated shadows
save
In certs - set bundle ID , and name .
save
Build ( production )
Package - ios - create new folder
Make a brew 
Save All
Launch all ios on …
on 5s and 6s have modulated shadows
but forgot to change content scale factor so 6s looks ugly … doh !
Window / Dev tools / Device Profiles
iPhone6 / rendering , add r.MobileContentScaleFactor = 2
Create new Profile iPhone6S
type = IOS
Parent iPhone6
iPhone6 / rendering , add r.MobileContentScaleFactor = 2
save as default
Save All
Package
Launch
6s now looks pretty and has modulated shadows , 5s sill has shadows
Save All
<4.9.2 part>
backup project folder
<4.10.pre2 part>
launch 4.10prev2
open project , convert in place
build
Save All
Package ios
( enjoy previously made beverage 
)
Launch
6s no modulated shadows . 5s black screen 
</4.10.pre2 part>
One thing I have also noticed is that the orange dot next to the game icon on myphone is nolonger there , but it was when launching from 4.9.2