HF communications are not easy, especially around India.
Two reasons.
First is that Mumbai still uses year 1942 issued Cossor radios.
Second is pilot's knowledge of HF is limited to "higher sun, higher frequency".
Might help you a little. I am a "Radio Ham" on 10, 20 and 40 meters bands...
xxx
First, let us talk of Stockholm Radio. Everyone knows them.
Get their website to get the current propagation chart.
Initial call, say where you are, so they turn their antenna to receive/transmit better with you.
xxx
Mumbai Radio (some of this applies to Karachi and Chennai)
On the chart, you see "MumbaI" then a few frequencies.
MID2 denotes frequencies common to Middle East HF stations group 2.
As an example, Karachi is among MID2 stations, so is Tehran, and Bahrain.
in Mumbai, the antennas for MID2 are oriented to favor the direction of that traffic.
And as you mentioned, "the higher the sun, the higher the frequency".
When you call Mumbai, tell them on which frequency you are transmitting.
The operator might be monitoring several radios, needs to know which one to answer you on.
Example "Mumbai, this is Speedbird 123 on 56, good evening". (56 for 5658) -
xxx
The other frequencies for Mumbai, i.e. AFI3 or INO1 might not be usable for you.
This because the frequencies are not monitored at the time, or wrong antenna orientation.
Happy contrails