You can really muddy the waters by arguing that an ejection pattern at x-o'clock means y just in and of itself, HOWEVER, generally speaking, if your AR is throwing brass forward a blue country mile (like noon to 2 o'clock or so), you could well be overgassed (or underweight with your buffer/spring, or...), from 2 o'clock or so through 4 o'clock or so is generally "ok" and arguably where you want it to eject, and from 4 o'clock or so to 6 o'clock undergassed (or too heavy a buffer or...). There's a stupid "chart"/"graph" of ejection patterns floating around that I won't both reposting here but it will give you a visual of basically what I just referenced.
That is a GROSS oversimplification and frankly doesn't always mean over/undergassed, but it could be some variation of multiple factors at play. For example, you could have an overgassed rifle with too heavy a buffer and XP buffer spring that ejects brass 1' from the rifle and stacks cases neatly at 3 o'clock. Does that means its operating optimally...NO. It is still overgassed, but you have applied said a "fix" for the symptoms instead of treating the disease, thus masking what was an overgassing problem from the get go with an overly heavy buffer/spring combo to get it to comply with a chart that says it should eject at x, y or z angle. At the end of the day, if your rifle/carbine is firing, ejecting, otherwise cycling properly and isn't beating the crap out of you, your brass, or your rifle/carbine components themselves, attempting to figure out whether it may be under or overgassed based on where its ejecting and how far away is a fool's errand at best.
Adding more reciprocating mass, etc., to an AR is NOT always the best way to go about handling certain issues, although it can help to reduce the aforementioned symptoms. As to folks who've never heard of XP springs and heavier buffers for rifle-length stocks (A1/A2/etc.)...they've been around a LOOOONG time now and actually can work to reduce perceived recoil, deal with increased blowback from suppressed fire, etc., but the best practice is still to deal with overgassing and/or recoil mitigation by tuning the gas system and not adding addt'l reciprocating mass, stiffer springs, etc. unless that's all you've got to work with for whatever reason. Furthermore, suggesting that adjustable gas blocks are merely for use on rifles/carbines that will see suppressed fire is in error. While they certainly work well in reducing gas volume in rifles/carbines that are subjected to considerably more blowback when shooting suppressed, the benefits of adjustable blocks go well beyond that single purpose.
As to the OP's situation, a rifle stock/receiver extension, 5oz rifle buffer and rifle spring, combined with an 18" barrel with a mid-length gas system that feels like it is cycling "kinda harsh" lends itself to assessing an overgassing situation regardless of where its throwing brass (12 o'clock or 6 o'clock) or how far away its throwing it (3' or 20'). BUT, with an 18" barrel and a mid-length gas system though (regardless of stock/receiver extension setup), the recoil impulse may tend to surprise some shooters as it will be somewhat sharper or a little more snappy than other platforms, especially 18" tubes with rifle-length gas systems, but that can vary wildly as well depending on what size gas port the barrel in question has got (there is no universal standard for gas port diameter by barrel length/gas system length/etc.), etc., etc.
Its not a simple matter of ejection at x-o'clock means its over/under/normally gassed.
