halacha - How long do you really need to keep your sideburns?

I've seen multiple sources that seem to indicate that one MUST keep his sideburns to either

1. The bottom of the ear


2. The bottom of the ear cartilage


3. To the jaw bone, around the middle of the ear.

When looking this up online, I came across this psak halacha from R' Abadi, in which he indicates that one who shaves with an electric shaver need not worry about any of this and only needs to leave a few rows of hair remaining in the payos area.

Is this a valid option? Is the practice to keep the sideburns long, as most yeshivishe people do, just a chumra?

Answer

All sources from Shulchan Aruch - Yoreh De'ah - 181

Regarding the shaver in the Payos area:

ג: אֵינוֹ חַיָּב אֶלָּא בְּתַעַר. וְיֵשׁ אוֹסְרִים בְּמִסְפָּרַיִם (ב) כְּעֵין תַּעַר, וְיֵשׁ לָחוּשׁ לְדִבְרֵיהֶם. ‏

באר היטב (ב) כעין. שגוזז במספרים סמוך לבשר כעין תער. ש''ך: ‏

As Matt pointed out, it's a matter of dispute. The Shulchan Aruch brings 2 opinions:

1. 
   

   It's only forbidden to use a razor.

   
   


2. 
   

   Even using scissors is forbidden. (When cutting close to the skin, not trimming, as per the Be'er Heitev.)

   
   

The Shulchan Aruch votes for the second opinion; he wouldn't approve of shaving in the Payot area.

As opposed to the beard area where only a razor is forbidden.

י: אֵינוֹ חַיָּב עַל הַשְׁחָתַת פְּאַת הַזָּקָן אֶלָּא בְּתַעַר, אֲבָל בְּמִסְפָּרַיִם מֻתָּר, אֲפִלּוּ כְּעֵין תַּעַר. ‏

As to "leave a few rows of hair remaining in the payos area" (and the area defined as Payot):

The Shulchan Aruch says that the area includes all the hair in line with the forehead and the ear, until the bottom of the ear where the jawbone gets wide.

"In this entire area one should not touch". This makes it sound like he wants one to leave all the hair intact in that area.

ט: שִׁעוּר הַפֵּאָה מִכְּנֶגֶד שֵׂעָר שֶׁעַל פַּדַחְתּוֹ וְעַד לְמַטָּה מִן הָאֹזֶן, מָקוֹם שֶׁהַלֶּחִי הַתַּחְתּוֹן יוֹצֵא וּמִתְפָּרֵד שָׁם, וְכָל רֹחַב מָקוֹם זֶה לֹא תִּגַּע בּוֹ יָד. ‏

The Kitzur Shulchan Aruch 170:1 also seems to understand it that way.

סימן קע - אסור גלוח פאות הראש והזקן

סעיף א': פְּאוֹת הָרֹאשׁ הֵן שְׁתַּיִם בְּסוֹף הָרֹאשׁ, וְהוּא מְקוֹם חִבּוּרוֹ לַלֶּחִי מִיָמִין וּמִשְׂמֹאל אֵצֶל הָאֹזֶן. וַאֲפִלּוּ לְגַלְּחָן בְּמִסְפָּרַיִם כְּעֵין תַּעַר, דְּהַיְנוּ סָמוּךְ לַבָּשָׂר, שֶׁאֵינוֹ מְשַׁיֵר כְּלוּם מִן הַשְּׂעָרוֹת סָמוּךְ לַבָּשָׂר, יֵש אוֹסְרִין. וְלָכֵן אִם צָרִיךְ לְגַלְּחָן לִרְפוּאָה, יִזָּהֵר שֶלֹּא לְגַלְּחֵן סָמוּךְ לַבָּשָׂר מַמָּשׁ. וְשִׁעוּר הַפֵּאָה מִכְּנֶגֶד שֵׂעָר שֶׁעַל פַּדַּחְתּוֹ וְעַד לְמַטָּה מִן הָאֹזֶן, מְקוֹם שֶׁהַלְּחִי הַתַּחְתּוֹנָה יוֹצֵאת וּמִתְפָּרֶדֶת שָׁם. ‏

The קיצור ש''ע ילקוט יוסף in 181:4 also frowns on shaving that area.

ויש אומרים שאיסור מקיף הוא גם במספריים כעין תער, ויש לחוש לדבריהם.

It would seem that R' Abadi is relying on the opinion that the Shulchan Aruch - and summaries thereof - mention, but they all say one should choose the other opinion.

You ask:

Is this a valid option?

Seems to be, as everybody mentions it.

Is the practice to keep the sideburns long, as most yeshivishe people do, just a chumra?

Not in the usual sense, as the Shulchan Aruch tells one to behave that way. Usually we'd define a Chumra as following a minor opinion, not one the Shulchan Aruch prefers.