Can you give a location where to observe it or/and upload a video?

Ok I've amended this ticket. My apologies for wasting your time - it was my mistake - I still had a mod loaded that caused the water splash particle/decal issue.
This morning I tested the function on 40+ maps with different texture scaling and settings and the function works perfectly and no snow impact water effect.

As far as the snow texture is concerned - I've attached two images showing the the default "a3\data_f\rainnormal_ca.paa" and the "a3\data_f\snowflake4_ca.paa" textures for comparison. Not surprisingly snowflake4_ca.paa texture looks best but not ideal when the texture is close to the camera. This is not critical but would be a nice to have improvement.

"a3\data_f\snowflake4_ca.paa" it means it has 4 flakes in it, you are using it as 1 flake

Thanks KK - excuse my ignorance in the context of BIS_fnc_setRain how do I reference the (presumably) first frame in the sequence of snowflake4_ca.paa? Like this?
// texDropCount isn't documented from what I can see.

After subsequent testing the answer is yes! Excellent thanks.

[
"a3\data_f\snowflake4_ca.paa", rainDropTexture
4, texDropCount
0.01, minRainDensity
15, effectRadius
0.1, windCoef
2, dropSpeed
0.5, rndSpeed
0.5, rndDir
0.02, dropWidth
0.02, dropHeight
[0.1, 0.1, 0.1, 1], dropColor
0.1, lumSunFront
0.1, lumSunBack
5.5, refractCoef
0.3, refractSaturation
true, snow
false // dropColorStrong
] call BIS_fnc_setRain;

I've updated documentation yesterday

rainDropTexture: a3\data_f\snowflake4_ca.paa - texDropCount: 4
rainDropTexture: a3\data_f\snowflake8_ca.paa - texDropCount: 8
rainDropTexture: a3\data_f\snowflake16_ca.paa - texDropCount: 16

Yes I saw you updated the biki thanks a lot KK. Quick question - is there a particleshape equivalent to the texture "a3\data_f\snowflake4_ca.paa" that can be used in setParticleParams?

It should work with setParticleParams, why, it doesnt? or you mean 3d particle?

I thought setParticleParams (and drop) would only take a p3d as input. I searched through many pbos but can't find a snow p3d or way of using the above "a3\data_f\snowflake4_ca.paa" texture in a particle script. Excuse me taking up your time.

No it is billbord type, a flat texture that oriented to face you at all time

Yes but how to pass the paa to setparticleparams:
particleSource setParticleParams
[
[

		particleShape,			/* String */
		particleFSNtieth,		/* Number */
		particleFSIndex,		/* Number */
		particleFSFrameCount,	/* Number */
		particleFSLoop			/* Optional - Number. Default: 1 */

],
animationName, /* String */
particleType, /* String - Enum: Billboard, SpaceObject */
etc
];

If I set particleshape to "", and "animationName" to "a3\data_f\snowflake4_ca", - the biki says N/A String - obsolete parameter that was meant to play .rtm anims, will throw "Skeletal animation not supported for particles" rpt error if not empty.

If I enter just "a3\data_f\snowflake4_ca", into the particle shape it throws an error and crashes the game : "Warning PreNLOD format..."
Excuse my stupid questions. But I just can't seem to pass just a paa to setParticleParams.