If you use (height loss requited x 2) + a "factor" = miles to touch down
you can work a TL closed descent profile, even in most exec jets.
NOTE: The "factor" varies according to weight and wind component and if you have to be fully configured by 5 miles or at 20 miles to touchdown.
EG
Top of Descent FL450
Bottom of Descent 0 feet
45x2=90
Plus a factor of say 30 = 120 miles This would be your TOD if you don't have excessive weight or a high tail wind component in the descent.
So how do you actually fly this?
Well at TOD you close the TL's and steadily increase the VS as you descend to maintain barbers pole -20kts or around 300kts IAS. NOW, here's the magic. You never want to be closer in track miles to touchdown in NM's than (Alt x 2) +15. If you are, you will likely need to use the speed brake at some point. If you are more than (Alt x 2) + 25 you will need power in the descent at some point... or wait till you level off at 5000 feet 25 miles out and drag your ass in using power
So once established in the descent, you adjust the VS to keep you around (Alt x 2) +20 = track miles to touchdown. If you are closer increase ROD. If you are further out reduce ROD.
I'm giving you a simplified version here. But this method keeps the T/L's closed and allows you to vary VS to maintain an efficient profile. So at 15,000 feet you could end up with a calculation of 15x2+15= 45 miles, so that's the point you now plan to slowly switch to the 3 degree profile. However you will have excess energy, so assuming obstacles aren't an issue, you can descend below your 3 degree profile, build in a slow down period at your level off alt, and recapture the 3 degree profile, without excess energy.
Always keep an accurate track miles to touchdown and you will always have a good indication of your energy state. It takes time getting used to, but it works.
Most Auto Throttle systems will fly a path and vary the speed, using thrust so you get throttle pumping all the way down the descent, which personally i hate.
Anyway, as i said, this is the short version and I'm happy to explore it more if you like.
All the best