On these Aero engines are the intake and exhaust valves open at the same time?
Radical Valve overlap to increase scavenging and bring resonance charging into play is only practically possible with multipoint direct injection as otherwise there is too much fuel-air mixture loss. There was a little overlap on the Merlin but obviously they didn't want to blow the mixture out.
The radical inlet vs exhaust valve overlap was introduced with the DB601E, it also required variable length inlet ports since there is a resonance like "trumpet" effect and the ports had to be lengthened at low rpm to facilitate starting and idling. The DB605A was a Slightly enlarged DB601E with the same bore centres and a new bearing and lubrication system.
Nice article here:
Daimler-Benz
And a comparison with Merlin, DB601A and DB605E here:
As you can see even the Merlin had 43 degrees overlap which is 1 degree more than the 42 degrees of the DB601A but nowhere near the 105 degrees of the DB601E.
Obviously water injection allowed Daimler Benz to get the charge cooling effect before the supercharger without giving up the radical valve overlap that would blow out fuel.
I think the resonance effect actually compressed the air in the cylinder by creating a standing wave node in the cylinder head.
Another reason for water injection was "internal cooling". I recall that in testing of the Ju 388 with the turbo-supercharged BMW 801TJ long climbs that an overstepping of cylinder temperature of 7C or so could occur presumably due to inadequate external cooling flow and that MW0 or MW50 was recommended to keep the heads within authorised limits. This was not to prevent preignition or allow increased boost.
Note for their BMW 802 engine BMW was planning on introducing variable timing on the exhaust valve since I don't think altering inlet port length is practical on a radial engine. Also exhaust pipes are also of varying length.