BL Touch / Source code tech help needed

Fitted a BL touch to my Ender 3 V2 using Youtube vids, modded source code to enable Touch etc. However when I select "Level" from the printer display the print head does the following.Moves to @XY 0 & homes to XY end stops, Z rises a few mm. Head moves to mid-bed & Z rises a few mm, a pause then Z rises another few mm. Then returns to near XY home, but with the Touch probe over the bed. The touch extends its probe & the head starts lowering, but the head is so high up by now that while it does lower down a fair way, as it nears the bed it gives up before the probe touches the bed. Does anyone have an idea where in the code this operation is configured in the Marlin source 2.0.x. (assume its the G29 sequence). I have had a root through looking for variable names to see if there is anything obvious I can tweak but no joy yet. Hoping to mod the "Level" start sequence to reduce the Z rise, or set the head to lower more distance before giving up.