Pricing is complicated, as you can influence on them through many many methods.
1°) to have the same price for all flights on a same route, go to Routes -> Price management -> Route Pricing, select the 2 airports in question, reset, and then increase if you want.
2°) When you're getting big, micromanagement becomes a pain in the back, and what I personally do is to reset prices every 3-4 years and then have a large and long adjustment/micromanagement campaign. For all my new routes, I don't bother and usually leave them at std price.
3°) To increase the price on all flights of a single route, you can also do Manage Routes -> Destination View (on the right, above the results), so you'll have the LF and such other things. If you increase prices, this new price will be based upon the default price (because you could have different pricing, so the system has to chose something to base upon, and not add 10% to 230 and 10% to 243, etc.).
4°) High LF is the easiest indicator to know if a route can be up-priced, however on a route at 70% LF with Std pricing, the highest income you could get could very well be at 65%. So even medium LF routes' tariffs can be increased a bit.
5°) A 3% increase from default pricing gives a slight bonus in transported pax, which is very interesting. There could be a reason, but I don't see one. Though if you don't want to bother, just reset and add 3%, the result will be better than with +5% (because at +5%, you'll transport pax paying more, but less pax overall, so less interesting).
6°) Ideally, you want the supply to be around 90% of the demand, so you can milk your passengers, +15, 20, or even 25% more than default. This one is clearly better than the 3% I just talked about.
7°) Not your case in LHR, but just know that HD seating can't support high overpricing. +15% is usually the max, with high CI and RI, before too many pax prefer not to fly with you (or not to fly at all) and your profit begins to drop.