you had enough light. Sadly, at 140" diagonal + and at maximum Throw distances, you do not.
As I mentioned, make the right choice as far as the Screen's coating goes, and your Contrast enhancement will far outstrip any loss of same due to increased brightness.
That Sir, has been a primary truth since MMud-SE (Silver Edition) and RS-MaxxMudd came into being, and got stupid better with the advent of Silver Fire.
Max Throw at 140" is 28" (5" retained) @ just 13 FL. Achieving deeper blacks by attenuating incoming light "BEFORE" it hits the Screen's surface is Robbing Peter to pay Paul. You do so ONLY as a last resort. The image you work with must depend upon light...not the lack thereof. It's a unfortunate testimonial to backwards logic that JVC chooses to tout low light output as a solution...which makes them the odd Mfg out these days. Also, just because they have a super wide Throw ratio does not mean the extreme end of it is usable.
At the Minimum Throw + 7" additional, your Foot Lambert jump to 20 fl. And you'll need it all since because your Zooming to achieve Scope, a good 2/5 ths of your available Lumen output is lost....poof.
While at 15' throw and 20 fl that equates to a drop of 8 fl to 12 fl off screen....at 28' and 13 fl you'd bottom out (...and I do mean crash...) at just 7.5 fl
Now all of this is based upon a 1.0 gain surface. Lets say instead you have a 1.3 gain surface that also greatly enhances perceived Contrast by deepening Blacks while retaining the perception of having pristine Whites and Dynamic Colors. I'm telling from direct experience with the RS-56 that it's JVC-caliber 90K:1 CR will look like JVC rated 250K:1.
At 11.3 gain and 15' you'd jump to 25 fl before cropping....at 28' you'd be up to 17 fl At those levels you can start to play with the Iris if you just have to.
No CaCa there! Been there, seen that a whole bunch, as has so many others.
Making yourself a viable High Gain / High Contrast screen is your best solution here....just embrace it.....