The rule on the height diference is answered on the SAA web site:

Q. Is the altitude/distance penalty the same for the Diamond Distance
as for the Gold Distance?
A. Yes. For all flights over 100 km in distance, the loss of height
between the Start and Finish cannot exceed 1000 meters (3281 feet). If
it does, the distance is reduced by 100 times the excess over 1000
meters.

Q. How does the penalty work?
A. Here is an example:
Release altitude + 8,200 ft msl
Finish point - 4,000 ft msl
Difference + 4,200 feet

Allowance - 3,281 feet
Difference + 919 feet

919 x 100 = 91,900 feet
91,900 / 5,280 (ft. in a mile) = 17.4 miles.

The penalty of 17.4 miles must be deducted from the distance flown over
the course. The adjusted course distance must exceed the required
distance for the task. The required distance for the Diamond Distance
leg is 500 km (310.7 miles).


Chris Reed wrote:
From memory the rule is 1% of the flight length as the maximum excess
of start height over finish height. So you'd need to start no higher
than 5,000 metres (roughly 16,500 feet) above the finish. Check this out
in the Sporting Code (fai.org) but looks fine to me on the numbers you give.

I fly in the UK flatlands, so if I ever fly one of my planned 500k
flights the difference is not comething I'll need to worry about.

303SAM wrote:
Need some help getting clear on terms, please.
I'm planning a Diamond Distance flight of 326 miles. The starting airfield
is at 300' msl. The finish will be at an airfield elev 1150' msl. If I
take a tow to 2300' msl, notch the baro, climb to 5000' msl and then cross
the start line am I penalized?

The safe and easy answer (I think) is to tow to no higher than 4431' (finish
height + 3281), release behind the start line, notch and cross the start
line, then climb up and start in earnest, but I'd like to be clear on the
terms. Is the height difference measured from tow release to finish or from
altitude when crossing the start line to finish?

Is an other safe answer to tow to 2300msl behind the start line, climb to
whatever altitude I can, and declare the release to be the starting point?