I told myself that I wouldn't get bogged down with minutiae over this chart as the Whole Wide InterWeb will never completely agree with me, nor was the chart originally intended for anyone but myself. But dbkita has valid concerns over a detail that I feel is the most debate-able point of the entire chart. In short, I've spent a lot of time considering it.
First off, I completely agree with you dbkita. I was/am on the fence about including the blue arrow. As of now, I think LR frigates do 75% damage vs. heavy cruisers and don't have good survivability. The reasons I am choosing to include the disputed blue arrow are as follows:
A ) This is a personal quick reference chart designed to aid me in the heat of battle i.e. I use this strategy. No one else has to. I feel strongly enough to leave it in, but others are welcome to reproduce the chart and take it off or reject my assessment all together. Quantifiable data is different than defining the quality between words like "good" and "great". This makes my opinions easier to defend, which is why I even submitted this to the internet in the first place. Take any strategies offered from someone with a grain of salt, as they may not be good for you or even all situations.
B ) Heavy Cruisers are inherently difficult to counter based on their stats and I didn't want to chart their "invulnerability" because that helps nobody fend them off. On that token, Long Range Frigates do the same percentage vs. Support CR as they do heavies. I left this data off because of my intentional chart simplicity and also because their damage type isn't that good in the first place vs. cruisers and there are two counters already listed against support (Light Frigs and Heavies).
C ) Support cruiser abilities are useful in countering heavies, but my "disclaimer" negates the consideration of abilities on this chart. I also wanted ships/structures to be generally effective at killing or staving off the countered ship and there is more micro involved in Support Cruisers countering Heavies. For that reason, I chose to give the credit Darvin3 gave to the Support CR to the ones dealing the damage.
D ) The red arrow pointing from Heavy Cruiser to Long Range Frigate should also be an indicator of how effective the reverse counter should be.
E ) My little "disclaimer" on the chart says the rest. Use combinations. Use angles, speed, build time, resource cost, research, and individual race strengths to your advantage. Micro does wonders. Attacking fleet composition is also a huge difference when considering the scenario you mentioned. This counter may not be effective if outsmarted by a better counter or even just a well-balanced fleet.
Happy hunting and I hope the chart helps. I don't believe I'll be making any more adjustments. I hope it helps the Sins community which has made me a better strategist in this amazing piece of gaming. I'd love for it not to have flaws, but anything someone produces that isn't a recitation of cold numbers will be arguably accurate depending on the recipient.