I used the MS and LD2 on the bars for a few rides, and I kept wondering why the LD2 wasn't working. It was working, but the light was drowned out by the MS.
I've been around block since I've posted to this thread
(that wont die!!!! %^%&#) See my earlier post....
I am now riding with a MS and Fenix LD20 for backup and a cheap helmet light. ($20 at target by energizer)
I did some comparison testing and discovered that the LD 20 does indeed "show up" as long as the MS in on its low setting. However the MS on medium or high completely snows over the LD 200 and older Dinotte 160s.
And although the LD20 is a generously wide beam, the MS is still larger. (too large for my taste - I'd rather have more throw)
Not that this matters to anyone else, I can use my Dinotte batteries with the MS giving me oodles of convenience and run time.
Here's the deal - about the actual OP - whether to "flood" or "spot." In real life, unless you run a really high power light, like at least 400-500 lumen, then you should have an axillary spotting light for some of the incidental situations. Too often a street sign will be too high or too wide for a normal beam to catch.
Another big factor is when animal or autos are approaching from an angle. Currently my setup allows me to "flash oncoming" objects that at an angle to me to assure that they see me. A typical case could involve a fork in a road or deer or a dog coming from the side.