U2715H, P2414H, daisy chaining (duplicate thread)

I'm having problem with daisy chaining U2715H REV A.05 (Nov 2017). I have recently bought a U2715H and I want to daisy chain it to my old P2414H (REV A.06, Oct 2015).

When I connect my old rig with Gigabyte GTX 760 OC 2GB (1x DP, 1x DVI-I, 1x DVI-D, 1x HDMI) via DP to DP on U2715H, and enable DP 1.2 to connect to P2414H via DP resolution on U2715H drops to 2048x1152@60Hz and P2414H works on native resolution 1920x1080@60Hz.

If I disable DP 1.2 on U2715H then on P2414H I get (of course) the message: "The current input timing is not supported by the monitor display. Please change your input timing to 1920x1080, 60 Hz or any other monitor listed timing as per the monitor specifications."

After all combinations with cables, driver updates (currently on last nvidia driver 398.11), problems with custom resolutions, refresh rates (to reduce bandwidth), etc... I realised that I haven't tried DP-->mDP because my rig is ~4m away from desk and my monitor setup and supplied mDP cable is 2m. I moved setup closer to connect and tried. And this worked but don't know why!!

I connected PC via DP > to U2715H mDP (in) --> DP to DP (on P2414H) and I got the full resolution on U2715H 2560x1440 @ 60Hz (native) and full resolution on P2414H 1920x1080@60Hz. For that I used the mDP-DP cable supplied with U2715H.

I tried different DP-DP cables. 2m, 3m, 10m (certified DELOCK 4K 10m and 3m, up to 3840x2160@60Hz, DP cable 2m supplied with P2414H). But only option that works for now is when I connect PC via DP to mDP on U2715H (2m long) then from U2715H DP (out) --> DP (in) on P2414H.

First I tought that it was the GTX 760 bandwidth (max digital resolution 4096 X 2160), cable lenght, cable bandwidth 3840x2160@60Hz. Now I'm not sure why mDP works, and normal sized DP doesn't!!!

Gigabyte GTX 760 (spec): https://www.gigabyte.com/Graphics-Card/GV-N760OC-2GD-rev-20#sp

10m cable: http://www.delock.com/produkte/S_84862/merkmale.html

Do you know which type mDP-DP cable is supplied with U2715H? It's has a thinner insulation than DP. And why should the mDP(in) connector work better than DP(in)?

I was thinking to get one more U2715H, but now I'm not sure if the setup could handle it via DP. I still have an option to connect P2414H via DVI which works. But with resolution of one more U2715H I think it wouldn't work.

Option is try to find a DP-mDP cable at least 4.5m long.

Also I would like to mention on P2414H to get normal picture via DP in daisy chain I needed to turn off Image Enhance. Then the image was normal. If Image Enhance was on picture would be "too crispy", too sharp.

Please advise!