Forget managed descent, it'll leave you high when they give you a shortcut. First thing to do is to work out track miles to the field and direct miles then decide what figure between you think you really have. You need 3xheight (in 1000s) to descend on a 3 degree slope plus a mile per 20kts to reduce speed. If you aim to be at 2000ft agl on the glide at just under 7 miles at 180 kts you can calculate back to decide whether you're high or low. In most instances V/S is the best mode to use to ensure continous descent. 5 x groundspeed as a V/S will give you a three degree slope, adjust accordingly. OP DES will work if you're very high but is best avoided close to the ground if your company stipulates RoD restrictions close to MSA as it can lead to some very high RoDs.
Personally I think all you need is flap 1 prior to LOC intercept, then flap 2 gear down at 2000ft with subsequent selections according to speed requirement. In speed terms if you have anything over 180 kts when you hit the glide the aircraft will not slow down, especially with A. ICE on. Landing gear will be necessary to reduce speed. If you are level on the LOC you can maintain 250 kts until about 3 miles prior to the G/S as long as your prepared to take the gear at G/S*.
My personal favourite 'Get Out Of Jail' card is to select V/S -2900 with full speedbrake which will see the aircraft stabilise at the V/S with an airspeed of 260-270kts, which gives you a guaranteed RoD and a speed you can predict. If you're still to high then reduce the V/S to -500, get below 250kts and lower the gear then resume the V/S -2900. Speed will stabilise around the 220kt mark, which may require Flap 1 depending on weight but is within placard speeds. These figures generally work across the range, adjusted up or down by 10kts if its a 321 or 319.
Forgot to mention that you should always have Flap 1 out when you capture the glide slope. If you don't then the go around mode won't be armed. Selecting TOGA then leads to the very unpleasant FMA of TOGA / GS / LOC !!!!