diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
index 35f0fbe..81e1aa8 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
@@ -1163,9 +1163,16 @@ function coverageGuardBandwidthHz(mode = modeEl ? modeEl.value : "") {
   return Math.max(0, Number.isFinite(maxBw) ? maxBw : currentBandwidthHz);
 }
 
+function effectiveSpectrumCoverageSpanHz(sampleRateHz) {
+  const sampleRate = Number(sampleRateHz);
+  if (!Number.isFinite(sampleRate) || sampleRate <= 0) return 0;
+  // Keep a guard band at the spectrum edges; practical usable span is slightly smaller.
+  return sampleRate * 0.82;
+}
+
 function requiredCenterFreqForCoverage(freqHz, bandwidthHz = coverageGuardBandwidthHz()) {
   if (!lastSpectrumData || !Number.isFinite(freqHz)) return null;
-  const sampleRate = Number(lastSpectrumData.sample_rate);
+  const sampleRate = effectiveSpectrumCoverageSpanHz(lastSpectrumData.sample_rate);
   const currentCenterHz = Number(lastSpectrumData.center_hz);
   if (!Number.isFinite(sampleRate) || sampleRate <= 0 || !Number.isFinite(currentCenterHz)) {
     return null;
@@ -1215,7 +1222,7 @@ async function setRigFrequency(freqHz) {
 
 function tunedFrequencyForCenterCoverage(centerHz, freqHz = lastFreqHz, bandwidthHz = coverageGuardBandwidthHz()) {
   if (!Number.isFinite(centerHz) || !Number.isFinite(freqHz) || !lastSpectrumData) return null;
-  const sampleRate = Number(lastSpectrumData.sample_rate);
+  const sampleRate = effectiveSpectrumCoverageSpanHz(lastSpectrumData.sample_rate);
   if (!Number.isFinite(sampleRate) || sampleRate <= 0) return null;
 
   const safeBw = Math.max(0, Number.isFinite(bandwidthHz) ? bandwidthHz : 0);
@@ -1236,7 +1243,7 @@ function tunedFrequencyForCenterCoverage(centerHz, freqHz = lastFreqHz, bandwidt
 
 async function shiftSpectrumCenter(direction) {
   if (!lastSpectrumData || !Number.isFinite(direction) || direction === 0) return;
-  const sampleRate = Number(lastSpectrumData.sample_rate);
+  const sampleRate = effectiveSpectrumCoverageSpanHz(lastSpectrumData.sample_rate);
   const currentCenterHz = Number(lastSpectrumData.center_hz);
   if (!Number.isFinite(sampleRate) || sampleRate <= 0 || !Number.isFinite(currentCenterHz)) return;
 
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css
index 0581353..82c15c5 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css
@@ -1396,7 +1396,7 @@ button:focus-visible, input:focus-visible, select:focus-visible {
     font-size: 1.1rem;
   }
   .spectrum-edge-shift-left {
-    left: 0.28rem;
+    left: -0.7rem;
   }
   .spectrum-edge-shift-right {
     right: 0.28rem;
@@ -1539,7 +1539,7 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   transform: translateY(-50%) scale(0.97);
 }
 .spectrum-edge-shift-left {
-  left: 0.45rem;
+  left: -0.9rem;
 }
 .spectrum-edge-shift-right {
   right: 0.45rem;