Keep it steep
You need to be very clear about what technique they are suggesting. The runway at LCY is short. The only reason it is adequate is that, in general for the types approved for LCY ops, if you arrive steeper, the landing roll is shorter. Your "normal" landing distances are based on a 3 degree arrival. If you look at the same aircraft landing distances for a 5.5 degree arrival you will find that you need less runway (although you land with more of a crunch!). Thus it is a big no-no at LCY to try to "correct" the sight picture by dropping below the 5.5 degree glideslope and turning it into a 3 degree arrival on final, because you will use more runway that way - possibly more than there is available to you.
On the other hand, if you are worried about landing too long, then on very short final (already established at 5.5 degrees) you can aim for the piano keys which will involve a brief INCREASE to the approach angle to 6 degrees or more - and you will then probably see 4 reds. You will also probably pull off a rotten landing, and wonder why you tried so hard - after all, the certification numbers were all done for the glideslope that exists, and they do work if followed carefully.