Hey thanks.
well you should keep moving and use the map to your advantage. We enforced the old shooter games style which is strafing to dodge hits on yourself. You can also zoom out by scrolling so you actually have your whole screen to select an enemy you want to merge with. This allows you to even get over corridor gaps.
if you have a mouse you can set up hotkeys i would recommend you to set F on one of them. It makes it easier for you to do the merge.