docs: clarify EV deadline weighting and export rate behaviour

Two questions that came up while using the new fields: how binding the EV
charging deadline actually is (soft, but the default penalty outweighs the
energy cost by roughly forty to one, and the target is met tightly), and
why grid_export_rates can vanish from the saved config file (values equal
to the default are omitted; /v1/config shows what is effective) together
with when a partial export level pays off at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/akkudoktoreos/optimpost.md

@@ -240,6 +240,16 @@ the first one.
 Each rate is one more state in the genetic state space, which is why the default is deliberately
 coarse. `[1.0]` restores the previous all-or-nothing behaviour.
 
+When EOS writes its configuration file it omits every value that equals the field default, so a
+`grid_export_rates` of exactly `[0.25, 0.5, 0.75, 1.0]` disappears from `EOS.config.json` on the
+next save. The rates are still active - `GET /v1/config` shows the effective configuration, the
+saved file only shows the deviations from it.
+
+Whether a partial level is ever selected depends on the scenario. Exporting at full power in the
+best-priced slots is optimal whenever the stored energy has no more valuable use; a partial level
+pays when the export competes with a later, more expensive self-consumption and the right amount
+of energy falls between two whole slots.
+
 The exported energy of one slot is bounded by
 
 ```{math}
@@ -373,6 +383,15 @@ The deadline is a target, not a hard constraint: if the remaining time is too sh
 `min_soc_percentage`, the optimizer charges as much as it can and accepts the penalty. Check
 `result.EAuto_SoC_pro_Stunde` at the deadline slot to see what was actually achieved.
 
+In practice the target behaves as if it were binding. The default penalty of `10` per missing
+percentage point is roughly forty times the cost of the energy itself (one point of a 60 kWh
+battery is 600 Wh, some 0.25 EUR at 0.40 EUR/kWh), so the optimizer keeps the deadline whenever
+charging power and remaining time allow it. The soft formulation only exists so that an
+unreachable target degrades gracefully instead of failing the whole optimization.
+
+Note that the target is met *tightly*: the optimizer stops at the first SoC that satisfies
+`min_soc_percentage`, because every further kWh only adds cost.
+
 ### Flexible Consumers (Home Appliances)
 
 Each entry of `home_appliances` describes one consumer whose run the optimizer may place in time.