Interception Technique Help?

So first off I want to say thank you to everyone who has been practically holding my hand so far with this whole thing.

Secondly Id like to apologize for SOOOO many threads but Im trying to dive into this and learn and learning requires many questions to be asked by me

But to the point, I would like to know the different techniques for interception. Im using one now in which I get a contact and general heading, draw a angle from the contact through my u boat, then in the direction of his general heading (if he is going east and Im north, then I cut the 2nd leg through his course which I map out wiht a ruler)

Then I draw a circle representative of his speed (slow is 6knots so well use that) then where that circle intersects his course I draw one rep of my speed. (say hes doing 6 knots and I feel like doing 7 or 8 so I draw a 8 km circle) then I draw an angle where my circle meets the 1st leg of the "Big angle" then I make the Big angle match the little angle and i have my interception.

However ive noticed that

A) Im quite inaccurate some times and in many cases must re adjust my positioning and

B) that for contacts far out (over 600km or more) that I seem to have trouble

(pertaining to B: In my current campaign I just got a report of a TF heading SE at 8 knots, however he was ridiculously far away, but since I hadnt seen any action yet Id figure id try, what I did was draw a 200 KM circle for the TF speed and a 300Km circle for mine (seeing as how I thought if I divide his speed as I lay it on the map by 4 mine would need to be also) <--is this wrong? and if so what is the general rule of thumb for how close convoys / ships/ etc should be for intercepts, AND is there another more efficient and better way to do long range intercepts??

and anythign else you guys can teach me would be great

Casey